The present invention relates to a thermal transfer recording apparatus having dual modes, i.e., printing and erasing as required (hereinafter erasure mode is sometimes referred to as correction).
A prior art thermal transfer recording apparatus of the type contemplated by the present invention is a printer which includes an ink ribbon coated with a heat-fusible solid ink, a thermal head disposed to face a sheet of recording paper with the ink ribbon interposed and which is equipped with a plurality of resistive thermo-generating elements, and a drive circuit for supplying an appropriate amount of electric power to the resistive thermo-generating elements. The ink ribbon used in this printer has a solid ink layer supported on the surface of a film base made of a suitable material such as polyester. the solid ink melts at a temperature of about 150.degree. C. and above and provides increased adhesion in the molten state. At ambient temperatures, the solid ink is not sticky and will remain on the base without being transferred to the recording paper even if it is pressed against the latter with the thermal head. However, if it is heated with the resistive thermo-generating elements, the ink will melt and is transferred to the printing paper to produce desired characters. If the unused portion of the ink ribbon is pressed against the solid ink portion transferred onto the printing paper and if the solid ink is heated with electric power being supplied to the resistive thermo-generating elements in a smaller quantity than is supplied during ink transfer, only the surface of the solid ink layer fuses to cause the surfaces of the solid ink portions on the printing paper and ink ribbon to adhere to each other. If the ink ribbon is therafter separated from the printing paper, the solid ink layer is peeled off the printing paper, thereby achieving erasure of the printed characters.
The thermal printer of the type described above is a convenient device in that it enables characters to be printed on various kinds of printing paper and permits them to be erased as required in a simple way by slightly changing the quantity of power to be supplied to the resistive thermo-generating elements. However, this printer still has room for improvement in the following points.
If the temperature of the environment in which the printer is used varies considerably, it frequently occurs that the quality of printed characters deteriorates or complete erasure of them is difficult to achieve. The principal cause of this problem is that printing and correction are accomplished by different mechanisms. If the printing mode is used as the criterion for adjusting the quantity of power according to the environmental temperature, good results will not be attained in the correction mode. If, on the other hand, the correction mode is used as the criterion for adjusting the quantity of power according to the environmental temperature, good results will not attained in the printing mode.